The incorporation of rare earth ions of lanthanide series of elements with numbers ranging from 57 to 71 of the Mendeleev's periodic system in glasses has led to the development of optical fiber lasers and amplifiers. Current interest is directed towards erbium-doped fibers for the fabrication of non-planar light-emitting devices, such as optical fiber lasers and amplifiers emitting at 1.53-1.55 .mu.m signal wavelength. Although such non-planar light-emitting devices can advantageously be used in a variety of communications systems, there are many potential applications for light-emitting devices for which non-planar devices are not readily or conveniently adapted. For instance, it would be desirable to integrate planar devices emitting at 1.53-1.55 .mu.m signal wavelength with electronic and opto-electronic devices or structures. Such planar devices are desirable replacements for the non-planar devices, due to their compact nature and increased mechanical stability, and are likely to find applications in lightwave communications systems.
Recently it was shown that a planar optical device with a Fabry-Perot cavity may be formed by two reflectors and an active layer which is doped with a rare earth element selected from lanthanide series elements with numbers 57 through 71. See U.S. patent application Ser. No. 07/906,910 filed on Jun. 30, 1992 in the name of Feldman et al., now U.S. Pat. No. 5,249,195, which is incorporated herein by reference. The fundamental mode of the cavity is in resonance with the emission wavelength of the selected rare earth element. In such a device, the operating wavelength fully depends on the wavelength of emission from an implanted ion. In a specific example of the Feldman et al. invention, a Fabry-Perot microcavity, grown on a Si substrate, consists of two Si/SiO.sub.2 distributed Bragg reflectors (DBRs) and an Er-doped SiO.sub.2 active region. Er is incorporated into the center of the SiO.sub.2 layer of the cavity as optically active Er atoms in SiO.sub.2. The fundamental mode of the cavity is in resonance with the 1.55 .mu.m emission of a 4 f electronic transition of Er.sup.3+ atoms in SiO.sub.2. This leads to excellent emission characteristics, including the spontaneous emission intensity, spectral finesse and emission lifetime, as compared to a no cavity structure, e.g., to a structure having only a bottom reflector and a rare-earth doped active layer.
It is desirable to further improve luminescence efficiency of such planar optical devices.